1. Field of the Invention
This invention relates to an improved process for the conversion of synthesis gas, i.e. mixtures of gaseous carbon oxides with hydrogen or hydrogen donors, to valuable hydrocarbon or alcohol products, particularly gasoline or methanol.
In one aspect, this invention is particularly concerned with a process for converting synthesis gas to hydrocarbon mixtures rich in aromatics.
In another aspect, this invention is concerned with providing novel catalysts for the conversion of synthesis gas to hydrocarbon mixtures.
In yet another aspect, this invention is concerned with catalysts which exhibit increased water gas shift activity so that greater amounts of oxygen are rejected from the process as CO.sub.2 rather than as H.sub.2 O.
2. Description of the Prior Art
With the forecasted exhaustion of the crude petroleum resources of this country drawing nearer and nearer, increasing thought must be given to utilizing the existing vast coal reserves as a major source of energy. However, since the present energy requirements are based primarily on liquid fuels, especially gasoline, methods must be found to convert coal into usable liquid fuels if it is to become a major energy source.
Processes for the conversion of coal and other hydrocarbons such as natural gas to a gaseous mixture consisting essentially of hydrogen and carbon monoxide, or of hydrogen and carbon dioxide, or of hydrogen and carbon monoxide and carbon dioxide, are well known. Although various processes may be employed for the gasification, those of major importance depend either on the partial combustion of the fuel with an oxygen-containing gas or on the high temperature reaction of the fuel with steam, or on a combination of these two reactions. An excellent summary of the art of gas manufacture, including synthesis gas, from solid and liquid fuels, is given in Encyclopedia of Chemical Technology, Edited by Kirk-Othmer, Second Edition, Volume 10, pages 353-433, (1966), Interscience Publishers, New York, New York, the contents of which are herein incorporated by reference. The techniques for gasification of coal or other solid, liquid or gaseous fuel are not considered to be per se inventive here.
It would be very desirable to be able to effectively convert synthesis gas, and thereby coal and natural gas, to highly valued hydrocarbons such as motor gasoline with high octane number, petrochemical feedstocks, liquifiable petroleum fuel gas, and aromatic hydrocarbons. It is well known that synthesis gas will undergo conversion to form reduction products of carbon monoxide, such as hydrocarbons, at from about 300.degree. F. to about 850.degree. F. under from about one to one thousand atmospheres pressure, over a fairly wide variety of catalysts. The Fischer-Tropsch process, for example, which has been most extensively studied, produces a range of liquid hydrocarbons, a portion of which have been used as low octane gasoline. The types of catalysts that have been studied for this and related processes include those based on metals or oxides of iron, cobalt, nickel, ruthenium, thorium, rhodium and osmium.
The wide range of catalysts and catalyst modifications disclosed in the art and an equally wide range of conversion conditions for the reduction of carbon monoxide by hydrogen provide considerable flexibility toward obtaining selected boiling-range products. Nevertheless, in spite of this flexibility, it has not proved possible to make such selections so as to produce liquid hydrocarbons in the gasoline boiling range which contain highly branched paraffins and substantial quantities of aromatic hydrocarbons, both of which are required for high quality gasoline, or to selectively produce aromatic hydrocarbons particularly rich in the benzene to xylenes range. A review of the status of this art is given in "Carbon Monoxide-Hydrogen Reactions," Encyclopedia of Chemical Technology, Edited by Kirk-Othmer, Second Edition, Volume 4, pp. 446-488, Interscience Publishers, New York, N.Y., the text of which is incorporated herein by reference.
McGrath, in U.S. Pat. Nos. 2,637,739 and 2,754,314 teaches that metals or the oxides of metals in Group VIII of the Periodic Table can be employed, either alone or in combination with supporting materials, as catalysts for the Fischer-Tropsch conversion.
In U.S. Pat. No. 3,013,990, Breck discloses Fischer-Tropsch catalysts which comprise a zeolite molecular sieve containing iron, nickel, cobalt or oxides thereof in the internal absorption area of the zeolite molecular sieve. The use of natural zeolite molecular sieves such as chabazite, faujasite, erionite, mordenite, gmelinite, and the calcium form of analcite; as well as synthetic molecular sieves such as zeolites A, D, L, R, S, T, X and Y are taught by Breck. The metallic compounds are incorporated in the zeolite by ion exchange methods. None of these references disclose or suggest the transition metal cyanide complexes utilized as the catalysts of the present invention.
The following three patents describe processes and catalysts for the production of ammonia. They contain no disclosure or suggestion of the process of the present invention, i.e., conversion of synthesis gas to valuable hydrocarbon products, nor do they disclose the catalyst compositions or the methods of activation of the present invention.
Starke, in U.S. Pat. No. 1,306,862 describes the catalytic production of ammonia and cyanogen (C.sub.2 N.sub.2). The catalyst disclosed therein comprises an iron group metal, an alkaline earth metal (Group IIA of Periodic Table) and an alkali metal (Group IA of Periodic Table) and may be formed by mixing "sodium or potassium ferrocyanid" with "calcium or magnesium ferrocyanid" and subjecting those materials to decomposition at high temperatures, ranging between 1500.degree. and 1900.degree. F., in the presence of gaseous mixtures. A suitable gaseous mixture is 10% atmospheric air and 90% producer gas.
U.S. Pat. No. 1,363,392 of Clancy discloses a catalytic method for the synthesizing of ammonia from its elements. The catalyst is prepared by depositing calcium, barium, strontium or potassium "ferro- or ferri-cyanids" on a suitable support and heating in an atmosphere of nitrogen, hydrogen, or mixtures thereof.
In U.S. Pat. No. 1,439,291, also of Clancy, "alkaline metal cyanogen compounds" are activated for the production of ammonia by heating in the presence of ammonia gas. Examples of suitable cyanogen compounds are: K.sub.4 Cr(CN).sub.6 ; K.sub.3 Cr(CN).sub.6 CoCa[Fe(CN).sub.6 ].sub.2, K.sub.3 Mn(CN).sub.6, Ba.sub.2 Mn(CN).sub.6, K.sub.4 Mn(CN).sub.6, K.sub.4 Ce(CN).sub.6 and Sr.sub.2 Ti(CN).sub.6. None of the above references disclose or suggest the transition metal cyanide complexes utilized as the novel catalysts of this invention. Nor do they disclose the method of activating said catalysts. In addition, the above references do not teach that any of the catalysts disclosed therein are usable for the conversion of synthesis gas to valuable hydrocarbon or alcohol products.
Recently it has been discovered that synthesis gas may be first converted to oxygenated organic compounds and these then converted to higher hydrocarbons, particularly high octane gasoline, by catalytic contact of the synthesis gas with a carbon monoxide reduction catalyst followed by contacting the conversion products so produced with a special type of zeolite catalyst in a separate reaction zone. This two-stage conversion is described in U.S. Pat. No. 3,894,102, the contents of which are incorporated herein by reference. Attempts to convert synthesis gas over X-zeolite, base exchanged with iron, cobalt and nickel, are described in Erdol and Kohle-Erdgas, Petrochemie: Brennstoff-Chemie, Vol. 25, No. 4 pp. 187-188, April, 1972.
In addition, it has been discovered that valuable hydrocarbon mixtures may be produced by reacting synthesis gas, in the presence of certain heterogeneous catalysts comprising intimate mixtures of two components in which the first component is selected from the class of inorganic substances that have catalytic activity for the reduction of carbon monoxide, and the second component is an acidic crystalline aluminosilicate of which ZSM-5 is typical. Substantial quantities of liquid mixtures which are rich in branched paraffins and aromatic hydrocarbons and eminently suited for making high octane gasoline or petrochemicals are obtained. This development is described completely in U.S. Pat. No. 4,086,262 of Chang et al. (U.S. Application Ser. No. 733,982 filed Oct. 20, 1976), the contents of which are incorporated herein by reference.